This invention relates to a method and system for sending messages using low consumption portable tags that may be affixed to moving personnel or objects.
There are many situations in which it is required to alert or send messages to moving personnel. For example, in an office or hospital environment wherein members of staff move from one room to another, it is frequently necessary to send short messages to a staff member advising him or her, for example, of an incoming telephone message or an imminent appointment. One way in which this can be done is for each staff member to wear a portable tag which contains a memory for storing a unique identity which may be read by a respective interrogation device or reader located somewhere in each room. The tag may be provided with a buzzer for alerting the wearer of an incoming message shown on a display device in the tag. The portable tag transmits its ID at regular intervals to the reader so as to allow determination thereby of which portable tags are located in its vicinity. Whenever the person bearing the tag moves into a new room, his or her identity is automatically determined for onward transmission to a central tracking computer, which keeps a record of each person""s ID and his or her corresponding location.
The requirement that each portable tag must constantly transmit its ID to the interrogation device is undesirable because, by their very nature, the portable tags are miniature devices that are energized by a small internal power source such as a battery. The more data which is transmitted by each portable tag, the greater is the energy consumption and the more often the battery must be replaced.
Yet a further consideration must be borne in mind when data is transmitted using optical transceivers. For example, infrared (IR) transceivers are particularly suited for the kind of task in question and require an optically transparent path unencumbered by obstacles for effective data transmission. On the other hand, if even inadvertently optical transparency is maintained between one room and an adjacent room, then there exists the risk that a portable tag located in one room might transmit its ID to the interrogation device associated with a different, adjacent room. Such optical transparency might, for example, be the result of a dividing door between the two rooms being ajar; or owing to a window between the two rooms permitting infrared transmission therethrough.
Our co-pending Israeli Patent Application No. 126799 filed on Oct. 29, 1998 is directed to such a system which permits more than one portable tag to communicate with the interrogation device simultaneously. This desideratum clashes with the requirement to avoid collisions which, with IR transceivers is particularly onerous on account of the fact that it is difficult to detect collisions owing to the half-duplex communications protocol inherent in IR transmission. Such a requirement is met by assigning time slots for each of the IR transceivers and using polling techniques, thus allowing the interrogation device to address a portable tag at will by including the portable tag""s ID in the data stream transmitted thereby.
Such a system is thus highly versatile but at the cost of requiring a sophisticated data communications protocol. Furthermore, since a portable tag can be addressed at will, it must always be ready to receive data transmitted thereto by the interrogator. This requirement can be met by making the portable tag constantly active. However, bearing in mind that the portable tag is battery powered, this imposes an unacceptable burden on the battery. Alternatively, battery power may be conserved if the portable tag is normally dormant. However, in this case the portable tag must be xe2x80x9cawakenedxe2x80x9d by the interrogator before data can be received by the portable tag. This places yet a further overhead on the circuitry in the portable tag""s receiver, thereby increasing its cost.
When short messages are required to be transmitted to the tag in order to alert the bearer thereof to take certain action, for example, the quantity of data that needs to be transmitted to the portable tag is minimal. It is then possible to dispense with the requirement for independent free addressing of the portable tag. In such cases, the overhead associated with the sophisticated data communications in the system described in Israeli Patent Application No. 126799 may not be warranted.
It is thus an object of the present invention to provide a method for keeping track of objects in which the drawbacks described above are significantly reduced or eliminated.
It is a particular object of the present invention to provide an improved communications protocol suitable for use with IR transceivers allowing near simultaneous two-way communication between an interrogation device and a plurality of IR transceivers.
In accordance with a broad aspect of the invention there is provided a method for effecting bi-directional IR data communication between an object transceiver and a reader, the method comprising the following steps carried out by the object transceiver:
(One) transmitting successive data packets to the reader,
(Two) upon termination of a transmission of each of said data packets, opening a time window for receiving a transmission from the reader.
In accordance with a further aspect of the invention there is provided an object transceiver adapted for bi-directional IR data communication with a reader, the object transceiver comprising:
a transmitter for transmitting successive data packets to the reader, and
a timer responsive to termination of a transmission of each of said data packets, for opening a time window for receiving a transmission from the reader.
The invention also encompasses a reader for sending a message using IR data communication to a portable object transceiver, said reader comprising:
a receiver for receiving a transmission of a data packet from the portable object transceiver, and
a transmitter for sending the message to the portable object transceiver during a narrow time window opened thereby.
Furthermore, the invention encompasses a system comprising a server connected to a plurality of readers for sending a message using IR data communication to a portable object transceiver, wherein the server is adapted to:
(One) locate a respective one of said readers in communication with the portable object transceiver, and
(Two) send the message from the server to the respective reader for onward transmission to the portable object transceiver during a narrow time window opened thereby.
The object transceiver may be a portable battery-powered badge worn by movable personnel to whom short messages are to be communicated. In order to reduce the risk of data collision between different badges, each badge transmits for only 2 ms, successive data being transmitted after 60 seconds if the badge is stationary. In such case, the likelihood of two badges attempting to transmit during the identical 2 ms period is clearly negligible. When the badges move, the time interval between successive transmissions is randomly varied between 3 and 5 seconds. Thus, here too, the risk of two or more badges attempting to transmit within the same time slot may be sufficiently reduced. Obviously, conventional data collision techniques requiring re-allocation of time slots and re-transmission of data may be employed in the event that, notwithstanding efforts to the contrary, two different badge IDs are transmitted simultaneously.